
.div01 {
    width: 600px;
    height: 400px;
    margin: 40px auto; /*左右保持40个像素边距，然后居中*/
    font-size: 40px;
    background-color: lightgrey;
    color: navy;
    text-align: center;
    line-height: 400px;
    border-radius: 30px;
}

#btn01{
    display: block;
    width:50px;
    height: 30px;
    background-color: lightblue;
    color:navy;
    margin: auto;
}